The artboard is the area that can contain artwork that will print, but its size may not necessarily be the same as your current page size. For instance, your artboard may be A3 size but your print settings be A4 size.
You can display the page boundaries on the artboard by using the View > Show Print Tiling command. With page tiling showing, you can see which areas of the artboard are printable and which are nonprintable, as indicated by solid and dotted lines.
Printable area: this is the innermost dotted lines and the part of the page which will print on the selected printer.
Nonprintable area: is the area between the two sets of dotted lines, and is the nonprintable margin of the page. Many printers can't print right up to the edge of the paper.
Page edge: is the outermost set of dotted lines.
Artboard: is displayed as solid lines and represents the maximum area that is printable. Any objects that are off the artboard will not print, even though they are visible on screen. If desired, you can hide the artboard boundaries, by choosing View > Hide Artboards.
Canvas: the area outside the artboard where it is convenient to create, modify, and store artwork before placing on an artboard. Any objects placed on the canvas will not print, even though they are visible on screen.
To change an artboard's size do one of the following
The artboard becomes selected. Do one of the following:
Artboards represent the regions that can contain printable artwork. You can use artboards as crop areas for printing or placement purposes.
The artboards control the position of the printer's marks on your document and also defines the exportable boundaries of the artwork. Illustrator by default crops the artwork to the artboard's boundaries, but you can choose to crop the artwork to a preset crop area or to a custom crop area that you can define.
It is possible to have up to 100 artboards per document depending on size. The number of artboards can be assigned when first creating a document or you can add and remove artboards at any time. You can create artboards in different sizes, resize them by using the Artboard tool, and position them anywhere on the screen.